I have got my hands on an APC UPS and some HP gen8 server, installed apcupsd on CentOS 7, connected the USB cable and everything was working fine except for this very annoying issue I had: * power goes down (pull the UPS power cord). after some minutes the UPS battery threshold is triggered and the server shutdown procedure is launched by apcupsd. power goes back up (plug in the power cord) while the server is already shutting down but the shutdown sequence is not yet completed. RESULT: the server will not power itself up even if the correct setting is selected in BIOS (last power state or always on). If the power stays offline for enough time for the server to completely shutdown and for the UPS to also shutdown once the power goes back online the server starts up automatically like it is supposed to do. The only workaround I could think of to solve the issue is running a cron job on the router, which is running OpenWRT, to trigger wake-on-LAN for the server. I don’t really like this solution, it feels hackish but still I could not find a better way to make the damn server power on automatically all by himself. As for OpenWRT and wake-on-LAN, first of all install etherwake from LuCI or opkg: …

After upgrading my OpenVPN server to CentOS 7.5 I had trouble connecting to it. Specifically, I had two different issues: ** the laptop, which is running Fedora 28, was able to connect just fine but DNS resolution was broken. ** OpenVPN for Android was also connecting just fine but reporting a weird error: OpenVPN: tun tap invalid argument (code=22). The first one was caused by me because after the CentOS upgrade procedure was completed I also run yum autoremove which deleted dnsmasq; the solution was fairly simple, reinstall and reconfigure dnsmasq. For the second issue the solution was to enable comp-lzo and voilà, everything started working again.

Configuring this piece of poorly documented bloated shit Mozilla came up with was a huge pain in the ass, so excuse the colored language but I am fucking pissed. The idea was to finally implement a system to synchronize Firefox’s bookmarks across multiple devices without giving Mozilla all my personal data. After some minutes spent researching the subject on the interweb I found out the synchronization system is a huge clusterfuck comprised of multiple components: …

Today I had Ansible reporting an error on one of my CentOS machines while performing the usual upgrade procedure. I SSH’d into the host to check what was wrong and run yum clean all && yum update manually just to be greeted with the following error: rpmdb: PANIC: fatal region error detected; run recovery error: db3 error(-30974) from dbenv->open: DB_RUNRECOVERY: Fatal error, run database recovery error: cannot open Packages index using db3 - (-30974) error: cannot open Packages database in /var/lib/rpm CRITICAL:yum.main: Error: rpmdb open failed The solution to the issue luckily was fairly simple and quick: …

NFS allows to share files and folders over network and is much much faster than samba while using way less resources. To setup a NFS server on Fedora 26 install: $ dnf install nfs-utils Shared directories are listed in the following configuration file: --- # Syntax # <path> <ipaddr>(<option>) /home/user/Public 192.168.0.0/255.255.255.0(ro,sync) More information can be found here: Fedora NFS administration guide. In the above example, the the directory ‘/home/user/Public’ can be accessed by every client in the same LAN with read-only permissions. In case SELinux is active and enforcing rules some further configuration might be required: …

This does not really works, read this: https://nagg.eu/monitor-hard-disk-smart-status-in-python/ First of all install smartmontools, it has the same name on pretty much every distro: $ emerge -a1 smartmontools Proceed to edit its configuration file, at the bottom of the file there is a quick explaination of all the available parameters: cat/etc/smartd.conf --- DEVICESCAN -H -R 1 -R 5 -R 7 -R 10 -R 11 -R 196 -R 197 -R 199 -R 200 -m user@domain.tld -n standby,10,q Parameter -H tells smartd to check the result of overall-health self-assesment test which is pretty much useless, -R is used to specify a single SMART attribute, if its value changes a mail is sent to user@domain.tld. To send emails a MTA must be installed, in centos that is sendmail, in gentoo it is not strictly necessary to have a full fledget MTA installed, nullmailer will suffice. If it is not already installed: …

Every time I have to setup a software RAID in Linux using mdadm I forget something, this time I am writing it down once and for all (or at least I hope so). For the sake of simplicity I will use the creation of a RAID1 as example but this very same procedure can be applied for any other kind of RAID. RAID array creation 1. Partition the drives This step must be repeated for each drive of the array (/dev/sdb and /dev/sdc in my case). …

XFS just like EXT4 (I wrote a post about it last year) supports online defragmentation, to manage those volumes on CentOS and Fedora xfsprogs package is needed. Fragmentation level of XFS volumes can be checked with the command: [root@CentOS ~]$ xfs_db -c frag -r /dev/sdb1 actual 4491, ideal 4006, fragmentation factor 10.80% To perform online defragmentation of XFS volumes run the following command: …

DNSCrypt installation process is pretty simple since it is present in the repository, pdnsd on the other hand is missing, luckily compiling from source is not that hard. For the sake of completeness I will also cover the procedure to install DNSCrypt from source, alternatively yum install dnscrypt-proxy. Install the required dependencies and get the source code: [root@CentOS ~]# yum install gcc libsodium-devel libtool-ltdl-dev git wget [root@CentOS ~]# git clone https://github.com/jedisct1/dnscrypt-proxy.git [root@CentOS ~]# wget http://members.home.nl/p.a.rombouts/pdnsd/releases/pdnsd-1.2.9a-par.tar.gz pdnsd Compile and install: …

Fail2ban is a useful tool capable of mitigating brute force attacks performed against a multitude of services (ejabberd in our case). Configuration is split between a multitude of files: jail.conf defines which filters are active while the filters scripts are placed in ./filter.d directory. [root@CentOS ~]# vi /etc/fail2ban/jail.conf --- bantime = 1200 findtime = 1200 maxretry = 10 backend = auto [ejabberd-auth] enabled = true port = 5222,5280,7777 action = iptables-multiport[name=ejabberd, port="5222,5269,5280,777", protocol=tcp] logpath = /var/log/ejabberd/ejabberd.log --- [root@CentOS ~]# vi /etc/fail2ban/filter.d/ejabberd-auth.conf --- [Definition] failregex = ^=INFO REPORT==== ===\nI\(<0\.\d+\.0>:ejabberd_c2s:\d+\) : \([^)]+\) Failed authentication for .+ from IP <HOST> \({{(?:\d+,){3}\d+},\d+}\)$ ^(?:\.\d+)? \[info\] <0\.\d+\.\d>@ejabberd_c2s:wait_for_feature_request:\d+ \([^\)]+\) Failed authentication for \S+ from IP <HOST>$ ^.* Failed authentication for \S+ from <HOST>$ ^.* from <<"<HOST>">> failed with error: <<"inexistent-account">>$ ^.* from <<"<HOST>">> failed with error: <<"bad-password">>$ ^.* from <<"<HOST>">> failed with error: <<"badformed-jid">>$ ignoreregex = [Init] journalmatch = --- The first two regular expressions are for user authentication while the others are for administration panel login. Other useful commands are: …